In a step up transformer we step up the votage and reduce the current but ohm"S law say V=IR or voltage is directly proportional to current then howz it possible ?

Ohm's law doesn't apply to a transformer. As stated above, P=VI is applied to it. Or you can use this simplified equation Is:Ip = Vp:Vs where, Is = Current in the secondary coil. Ip = Current in the primary coil. Vs = Voltage in the secondary coil. Vp = Voltage in the Primary coil.

You're misinterpreting the transformer voltage / current relationship.

Step-up transformers (say 1:2 ratio) double the voltage, and halve the safe current potential of the transformer.

In power transformers, current isn't limited until the physical limitations of the transformer are reached. Beyond that point the transformer can't "keep up" and will limit current as it simultaneously starts to overheat (and fail...)

When you apply that doubled voltage to a device (resistor, whatever) it will still draw twice as much current as it did (at half the voltage.) Until the current potential of the transformer is exceeded, that is.

Ohm's law does and doesn't apply here. While the electrical resistance of the wire is subject to the law, in devices like transformers inductance / impedence are more important. You're not applying Ohm's law appropriately in this case (don't), use Power = Current x Voltage instead. E.g. 110 VAC @ 0.1 A = 11 Watts, converted to 12VAC you have 1.09 A.

active| newest | oldestplease go through the following link and get 100% clarification between transformer's principles and Ohm's law.

http://www.theijes.com/papers/v4-i2/Version-3/I423...

Ohm's law itself is not satisfying Law of Conservation of Energy under transformation.

with regards,

Ramkumar K

As stated above, P=VI is applied to it.

Or you can use this simplified equation

Is:Ip = Vp:Vs

where,

Is = Current in the secondary coil.

Ip = Current in the primary coil.

Vs = Voltage in the secondary coil.

Vp = Voltage in the Primary coil.

Step-up transformers (say 1:2 ratio) double the voltage, and halve the safe current

potentialof the transformer.In power transformers, current isn't limited until the physical limitations of the transformer are reached. Beyond that point the transformer can't "keep up" and will limit current as it simultaneously starts to overheat (and fail...)

When you apply that doubled voltage to a device (resistor, whatever) it will still draw twice as much current as it did (at half the voltage.) Until the current potential of the transformer is exceeded, that is.

inductance/impedenceare more important.You're not applying Ohm's law appropriately in this case (don't), use Power = Current x Voltage instead. E.g. 110 VAC @ 0.1 A = 11 Watts, converted to 12VAC you have 1.09 A.

L